What is Topological: Definition and 264 Discussions

In mathematics, topology (from the Greek words τόπος, 'place, location', and λόγος, 'study') is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing holes, opening holes, tearing, gluing, or passing through itself.
A topological space is a set endowed with a structure, called a topology, which allows defining continuous deformation of subspaces, and, more generally, all kinds of continuity. Euclidean spaces, and, more generally, metric spaces are examples of a topological space, as any distance or metric defines a topology. The deformations that are considered in topology are homeomorphisms and homotopies. A property that is invariant under such deformations is a topological property. Basic examples of topological properties are: the dimension, which allows distinguishing between a line and a surface; compactness, which allows distinguishing between a line and a circle; connectedness, which allows distinguishing a circle from two non-intersecting circles.
The ideas underlying topology go back to Gottfried Leibniz, who in the 17th century envisioned the geometria situs and analysis situs. Leonhard Euler's Seven Bridges of Königsberg problem and polyhedron formula are arguably the field's first theorems. The term topology was introduced by Johann Benedict Listing in the 19th century, although it was not until the first decades of the 20th century that the idea of a topological space was developed.

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  1. M

    I Chart coordinate maps of topological manifolds

    Hello every one . first of all consider the 2-dim. topological manifold case My Question : is there any difference between $$f \times g : R \times R \to R \times R$$ $$(x,y) \to (f(x),g(y))$$ and $$F : R^2 \to R^2$$ $$(x,y) \to (f(x,y),g(x,y))$$ Consider two topological...
  2. FallenApple

    Topology Introduction to Topological Manifolds by John Lee (prereqs)

    I'm interested in this subject. This is a graduate text and I believe the prereqs are mostly a math degree, which I somewhat have(B.S in Applied Math from a few years back). The thing is, I forgot details about things. For example, I know how to do an epsilon delta proof and can read one when...
  3. qnach

    I Crystal Structure Database (Pb0.5Sn0.5)Te

    I would like to find the crystal structure of (Pb0.5Sn0.5)Te I was told it is similar to NaCl basically an XY crystal I think it is called Space Group: 225 I would like to know the first, second, third ...layer of atoms closest to a X atom...and perhaps their distance... I found...
  4. L

    B Time reversal symmetry in topological insulator

    Hi all My question: I have read: Topological Insulators: Dirac Equation in Condensed Matters But also I have read: Observation of a Discrete Time Crystal Is it different situations ?
  5. B

    I Normed Vector Spaces and Topological Vector Spaces

    Let ##(V, ||\cdot||)## be some finite-dimensional vector space over field ##\mathbb{F}## with ##\dim V = n##. Endowing this vector space with the metric topology, where the metric is induced by the norm, will ##V## become a topological vector space? It seems that this might be true, given that...
  6. C

    Physics Is Topological Matter Worth Pursuing for a PhD?

    I went to an applied phd program in computational biology and got bored, so now I'm considering physics. Topological matter looks fancy/sort of interesting. Does it have anything to do with actual experiments (and I mean more than just insulators/superconductors) yet? I would assume that to...
  7. Math Amateur

    Charts on Topological Manifolds - Simple Notational Issue

    I am reading "An Introduction to Differential Topology" by Dennis Barden and Charles Thomas ... I am focussed on Chapter 1: Differential Manifolds and Differentiable Maps ... I need some help and clarification on an apparently simple notational issue regarding the definition of a chart...
  8. T

    Mathematical theory for topological insulators

    I have been learning topological insulators recently, and I become more and more curious about the link between topological insulators and mathematical theory these days. I know topological insulators have something to do with fiber bundles and K-theory. I have a relatively good background of...
  9. C

    Why is a branched line in R2 not a topological manifold?

    Is there a topologist out there that wants to explain why exactly a branched line in R2 is not not a topological manifold? I know it's because there doesn't exist a chart at the point of branching, but I don't understand why not. I'm just starting to self study this, so go easy on me :).
  10. M

    Is there an easy review about topological insulator?

    Hello. Is there a review paper about topological insulator which is written for non-physics major people? If it will be helpful, I know classical physics, basics about band theory and little bit of modern physics, and have just finished learning quantum mechanics (with a book written by...
  11. M

    Topological Insulator: A Zero-Gap Material With SOC?

    Hi every one, I face with a question on my works, As you know there in many articles Physicist introduce a material that has zero gap without spin-orbit coupling (SOC). By applying the SOC, a relatively small gap (0.1 eV) is opened and it becomes topological insulator. My question, Is that...
  12. SoumiGhosh

    Topological phase and spontaneous symmetry breaking coexist?

    As we know topological phases cannot be explained using spontaneous symmetry breaking and order parameter. But can they coexist? Suppose there is a system which is undergoing quantum phase transition to a anti-ferromagnetic phase from a disordered phase. So in the anti-ferromagnetic phase...
  13. ShayanJ

    Topological effects in Particle Physics

    I've been checking a university's descriptions of its research groups and their interests, where I encountered the phrase "Topological effects in Particle Physics" which had no explanation. I searched in the internet, but I couldn't find anything. Could anyone explain about such effects and...
  14. M

    Basic questions on Nakahra's definition of topological space

    In chapter 2.3 in Nakahara's book, Geometry, Topology and Physics, the following definition of a topological space is given. Let X be any set and T=\{U_i | i \in I\} denote a certain collection of subsets of X. The pair (X,T) is a topological space if T satisfies the following requirements 1.)...
  15. nuclearhead

    What kind of local topological "particles" can you get in R3?

    I know the solution for R2. That is a for an infinite plane you can have one of 2 things (from the classification of 2D surfaces): 1) cross cap (cut a circle out of the plane and identify opposite points). 2) a oriented handle (cut two circles out and identify points on one with reflected...
  16. A

    What is a topological phase transition and how is it characterized?

    I have just been reading a classical paper on the formation of majorana edge states (MES) in quantum wires. The hamiltonian is Kitaev type with a superconducting and spin-orbit interacting and one finds that the energies have a gap that closes and reopens as we vary the magnetic field. According...
  17. M

    Effect of TRS potential on Topological insulator (QSH)

    Hi every body, I faced a paradox. The topological insulator is robust against a potential that does not breaks the TRS. But in the original work of Kane-Mele (PRL 95, 146802), the "staggered sublattice potential" that does not breaks the TRS,, makes zigzag ribbon trivial insulator (figure 1 in...
  18. evinda

    MHB Topological Sort: Finding a Contradiction

    Hello! (Wave) The topological sort of a graph can be considered as an order of its nodes along a horizontal line so that all the directed edges go from the left to the right. How could we show that all the directed edges go fom the left to the right? We suppose that it is: Then it holds...
  19. M

    Topology required for topological quantum computing?

    I guess the usual answer would be to learn as much as possible. Some background about me: I am not a physicist but I'd like to pursue a PhD in theoretical physics (after a year or two) and work on topological quantum computing. I am familiar with quantum mechanics and solid state physics (at...
  20. PhysicsKid0123

    "Topological" properties of photons?

    I was wondering, how does a photon look like? What does it look like? I'm taking modern physics at the moment and I'm able to calculate lots of things quite well. Like DeBroglie wavelengths, I'm able to utilize the Schrodinger equation and the Heisenberg uncertainty principle and what not but I...
  21. H

    Self-learning topological insulator

    I would like to learn topological insulator. But what kind of reference should I look for. I just have some basic solid state physics knowledge. I know there are lots of Hall Effects (e.g. spin hall effect, quantum hall effect ...etc). and I just know the idea of them, but not the math
  22. V

    Topology of Relativity: Implications of Niels Bohr's Arguments

    I have seen in the online Stanford Encyclopedia of Philosophy in the entry on Copenhagen Interpretation of Quantum Mechanics that Niels Bohr had argued that the theory of relativity is not a literal representation of the universe: "Neither does the theory of relativity, Bohr argued, provide us...
  23. TrickyDicky

    Extended plane as a topological sphere

    The extended plane (E2 U ∞) is a non-orientable surface, and yet topologically is a sphere which is orientable, can someone comment on how this is reconciled?
  24. M

    Set inclusion in topological space

    Homework Statement . Let ##X## be a topological space and let ##A,B \subset X##. Then (1) ##A \cap \overline{B} \subset \overline{A \cap B}## when ##A## is open (2) ##\overline{A} \setminus \overline{B} \subset \overline {A \setminus B}##. The attempt at a solution. In (1), using...
  25. S

    Why the topological term F\til{F} is scale independent?

    why the topological term in gauge theory, ε_{\mu\nu ρσ}F^{\mu \nu} F^{ρσ} ,is scale-independent?
  26. A

    Nested sequence of closed sets and convergence in a topological space.

    Homework Statement Let ##X## be a topological space. Let ##A_1 \supseteq A_2 \supseteq A_3...## be a sequence of closed subsets of ##X##. Suppose that ##a_i \in Ai## for all ##i## and that ##a_i \rightarrow b##. Prove that ##b \in \cap A_i##. Homework Equations The Attempt at a Solution...
  27. A

    MHB A question on ergodic theory: topological mixing and invariant measures

    Hi All, This is a question on ergodic theory - not quite analysis, but as close as you can get to it, so I decided to post it here. Suppose I have a compact metric space $X$, with $([0,1], B, \mu)$ a probability space, with $B$ a (Borel) sigma algebra, and $\mu$ the probability measure...
  28. MattRob

    What is the Topology of a Tangent Bundle?

    Hello! I'm trying to teach myself some mathematics, and I want to see if I understand this concept correctly from what I've been reading. (And just to be clear, this isn't part of any coursework, so I assume it doesn't go under that section for that reason?) So, essentially, although...
  29. C

    Example of a topological manifold without smooth transition functions.

    In the definition of smooth manifolds we require that the transition functions between different charts be infinitely differentiable (a circle is an example of such a manifold). Topological manifolds, however, does not require transitions functions to be smooth (or rather no transition functions...
  30. E

    Properties of the Dirac point and Topological Insulators

    I understand that the centring of the Fermi energy at the Dirac point is a highly sought after property in Topological Insulators but I'm unsure as to exactly why? I see that the state at the conical intercept will be unique but I'm not sure of what is theorized to happen to the electrons...
  31. C

    Idea behind topological manifold definition.

    The usual definition of an n-dimensional topological manifold M is a topological space which is 'locally Euclidean', by which we mean that: (1) every point in M is contained in an open set which is homeomorphic to ##\mathbb{R}^n##. (2) M is second countable. (3) M is an Hausdorff space...
  32. C

    Topological indistinquisable points and set theory.

    In set theory a set is defined to be a collection of distinct objects (see http://en.wikipedia.org/wiki/Set_%28mathematics%29), i.e. we must have some way of distinguishing anyone element from a set, from any other element. Now a topological space is defined as a set X together with a...
  33. S

    Theoretical Research Topics in Topological Quantum Computing

    Can anyone suggest any? I have all of the coursework for a PhD, So I'm not afraid of anything but I will have lots of questions.
  34. S

    Topological Conjugation between two dynamical systems

    Find a topological conjugation between g(x) and T(x) where g and T are mappings (both tent maps [graphically speaking]) g:[-1, 1] → [-1,1] g(x) = 1-2|x| T:[0,1] → [0, 1] T(x) = 2x when x ≤ 1/2 and 2(1-x) when x ≥ 1/2 h ° T = g ° h (homeomorphism) h:[0, 1] → [-1, 1] h(x) = cos(∏x)...
  35. S

    Topological Conjugation between two dynamical systems

    Homework Statement Find a topological conjugation between g(x) and T(x) where g and T are mappings (both tent maps [graphically speaking]) Homework Equationsg:[-1, 1] → [-1,1] g(x) = 1-2|x| T:[0,1] → [0, 1] T(x) = 2x when x ≤ 1/2 and 2(1-x) when x ≥ 1/2 h ° T = g ° h (homeomorphism)The...
  36. D

    A topological space that is neither discrete nor indiscrete

    Homework Statement is it possible to have a topological space that is neither the indiscrete nor the discrete, and very set in the topology is clopen? Homework Equations The Attempt at a Solution let ##X## = {(0,1),(2,3)} with the ordinary topology on R. (0,1) is open, but...
  37. D

    Prove that a sequence converges in this topological space iff

    Homework Statement Consider (R,C). Prove that a sequence converges in this topological space iff it is bounded below define ##C = ## ##\left \{ (a,\infty)|a\in R \right \} \bigcup \left \{ \oslash , R \right \}## Homework Equations The Attempt at a Solution So I am not very...
  38. M

    Why topological invariants instead of topological invariances?

    Isnt it invariant an adjective?
  39. L

    What does vanishing at infinity mean for a topological space?

    If X is a locally compact Haussorff space, then the set of continuous functions of compact support form a normal vector space C_c(X) with the supremum norm, and the completion of this space is the space C_0(X) of functions vanishing at infinity, i.e. the space of functions f such that f can be...
  40. S

    Scattering in Topological Insulators

    It is well known that back-scattering of surface electrons in topological insulators is prohibited due to Kramer's degeneracy theorem as long as Time Reversal Symmetry is not broken by magnetic field or magnetic impurities. I would like to know what effect this has on scattering length and...
  41. R136a1

    Some questions about topological groups

    So, I have a topological group ##G##. This means that the functions m:G\times G\rightarrow G:(x,y)\rightarrow xy and i:G\rightarrow G:x\rightarrow x^{-1} are continuous. I have a couple of questions that seem mysterious to me. Let's start with this: I've seen a statement...
  42. F

    Where does the Berry phase of $\pi$ come from in a topological insulat

    The Berry connection and the Berry phase should be related. Now for a topological insulator (TI) (or to be more precise, for a quantum spin hall state, but I think the Chern parities are calculated in the same fashion for a 3D TI). I can follow the argument up to defining the Chern parity $\nu$...
  43. D

    What is the role of CdTe in CdTe/HgTe/CdTe Topological insulator?

    to get a 2D mercury telluride topological insulator, one has to construct a quantum well structure to get a bulk gap and most people use sandwiched structure with mercury cadmium telluride on top and the bottom. (so CdTe/HgTe/CdTe) and my question is can we get same or similar quantum...
  44. R

    Is a Topological Action Defined by the Underlying Space?

    Hi, I have a simple question: What is a Topological Action?
  45. P

    Topological Data Analysis - Persistent Homology

    Hi, I am not a mathematician, but I have noticed some recent papers on this seemingly new field, called Topological Data Analysis (see this relevant paper). I have had an overview of the applications and it seems that when you have data points that were sampled from some source (e.g. an...
  46. T

    Topology of the Set {1/n} for Positive Integers Z

    Determine the interior, boujdary, and closure for the set: { 1/n : n is in the positive integers Z}. Attempt: two things bothering me. 1) if i am in the set of positive integers, how does 1/n even exist? 2) now let's say it does exist, then the inteior would be empty because every...
  47. C

    Questions on Topological Insulators, confused on some terminologies

    Hi all! I am currently reading stuff related to quantum hall effect and topological insulators, and have a couple of questions. 1. I read about that band insulators can be classified into two types: topological trivial insulators and topological non-trivial insulators. And there is a...
  48. H

    Topological property of the Cantor set

    Let X be a metric separable metric and zero dimensional space.Then X is homeomorphic to a subset of Cantor set. How can it be proved? Thank's a lot, Hedi
  49. E

    Fabrication of topological insulators

    Hi I have been searching some papers online to find how practically we can approach for the fabrication of topological insulators. Can somebody please help me regarding this by providing some web links or some insight on the fabrication of topolopgical insulators...
  50. I

    Changing the orientation of a connected topological space

    Say we have a disconnected manifold with components C1, C2, C3. (I know in the threat title I said just topological space, but I'm actually thinking of manifolds here, sorry! Not sure how to change the title) It makes intuitive sense that if we're looking at just one of the components, then...
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